The present invention pertains to cardiac pacing systems that pace and sense in at least a first site in the heart and sense conducted electrical signals at a second site in the heart and measuring and accumulating electrical conduction times between the first and second sites to derive trend data indicative of the state of heart failure.
CHF is defined generally as the inability of the heart to deliver enough blood, i.e., to supply sufficient cardiac output, to the peripheral tissues to meet metabolic demands. Frequently CHF is manifested by left ventricular dysfunction (LVD), but it can have a variety of sources. For example, CHF patients may have any one of several different conduction defects. The natural electrical activation system through the heart involves sequential events starting with the sino-atrial (SA) node, and continuing through the atrial conduction pathways of Bachmann""s bundle and internodal tracts at the atrial level, followed by the atrio-ventricular (AV) node, Common Bundle of His, right and left bundle branches, and final distribution to the distal myocardial terminals via the Purkinje fiber network. A common type of intra-atrial conduction defect is known as intra-atrial block (IAB), a condition where the atrial activation is delayed in getting from the right atrium (RA) to the left atrium (LA). In left bundle branch block (LBBB) and right bundle branch block (RBBB), the activation signals are not conducted in a normal fashion along the right or left bundle branches respectively. Thus, in a patient with bundle branch block, the activation of the right ventricle (RV) and the left ventricle (LV) is slowed, and the QRS is seen to widen due to the increased time for the activation to traverse the conduction path. For example, in a patient with LBBB, the delay in the excitation from the RV to the LV can be as high as 120 to 150 ms.
Thus, cardiac depolarizations that naturally occur in one upper or lower heart chamber are not conducted in a timely fashion either within the heart chamber or to the other upper or lower heart chamber diseased hearts exhibiting LVD and CHF. In such cases, the right and left heart chambers do not contract in optimum synchrony with each other, and cardiac output suffers due to the conduction defects. In addition, spontaneous depolarizations of the LA or LV occur at ectopic foci in these left heart chambers, and the natural activation sequence is grossly disturbed. In such cases, cardiac output deteriorates because the contractions of the right and left heart chambers are not synchronized sufficiently to eject blood therefrom. Furthermore, significant conduction disturbances between the RA and LA can result in left atrial flutter or fibrillation.
More particularly, as described in commonly assigned U.S. Pat. No. 6,129,744, LVD and other forms of heart failure are manifested by reduced ejection fraction from the LV thereby reducing stroke volume and promoting pulmonary edema limiting the patient""s ability to exercise. Patients suffering from LVD are also known to have elevated levels of catecholamines at rest because the body is attempting to increase cardiac output that induce a higher resting heart rate. In addition, the QT interval for such a patient is affected by the catecholamine level and thus has a changed pattern during exercise as well. These patients have a decreased QT response, or smaller change in QT, during exercise, such that the QT interval shortening during exercise is smaller than that found normally. Although QT interval is influenced independently by heart rate alone, as well as by exercise and catecholemines, it is not known to what extent each of these factors or both are responsible for the changed QT response to exercise in LVD patients. However, it is known that patients suffering LVD clearly have a different pattern of QT interval shortening during exercise. Moreover, the changed conductive patterns or a heart in heart failure are manifested by other changes in the PQRST waveforms, particularly an abnormally wide or long duration of the ventricular depolarization signal, or QRS.
It has been proposed that various conduction disturbances involving both bradycardia and tachycardia of a heart chamber could benefit from pacing pulses applied at multiple pace/sense electrode sites positioned in or about a single heart chamber or in the right and left heart chambers in synchrony with a depolarization which has been sensed at least one of the pace/sense electrode sites. It is believed that atrial and left ventricular cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy, LVD and CHF.
A number of proposals have been advanced for providing pacing therapies to alleviate heart failure conditions and restore synchronous depolarization and contraction of a single heart chamber or right and left, upper and lower, heart chambers as described in detail in the above referenced ""744 patent and in commonly assigned U.S. Pat. Nos. 5,403,356, 5,797,970 and 5,902,324 and in U.S. Pat. Nos. 5,720,768 and 5,792,203. The proposals appearing in U.S. Pat. Nos. 3,937,226, 4,088,140, 4,548,203, 4,458,677, 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers is addressed in the ""688 and ""259 patents, as well as in U.S. Pat. Nos. 4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867.
The medical literature also discloses a number of approaches of providing bi-atrial and/or bi-ventricular pacing as set forth in: Daubert et al., xe2x80x9cPermanent Dual Atrium Pacing in Major Intra-atrial Conduction Blocks: A Four Years Experiencexe2x80x9d, PACE (Vol. 16, Part II, NASPE Abstract 141, p.885, April 1993); Daubert et al., xe2x80x9cPermanent Left Ventricular Pacing With Transvenous Leads Inserted Into The Coronary Veinsxe2x80x9d, PACE (Vol. 21, Part II, pp. 239-245, January 1998); Cazeau et al., xe2x80x9cFour Chamber Pacing in Dilated Cardiomyopathyxe2x80x9d, PACE (Vol. 17, Part II, pp. 1974-1979, November 1994); and Daubert et al., xe2x80x9cRenewal of Permanent Left Atrial Pacing via the Coronary Sinusxe2x80x9d, PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April 1992).
In the above-referenced ""324 patent, an AV synchronous pacing system is disclosed providing three or four heart chamber pacing through pace/sense electrodes located in or adjacent one or both of the RA and LA and in or adjacent to the RV and LV. During an AV delay and during a V-A escape interval, a non-refractory ventricular sense event detected at either the RV or LV pace/sense electrodes starts a conduction time window (CDW) timer. A ventricular pace pulse is delivered to the other of the LV or RV pace/sense electrodes at the time-out of the CDW if a ventricular sense event is not detected at that site while the CDW times out.
The above-referenced ""744 patent discloses a rate responsive, bi-ventricular pacemaker having one or more sensors for sensing a parameter indicative of the physiologic need for cardiac output, and for pacing the patient on demand between a lower rate limit (LRL) and an upper rate limit (URL). In a specific embodiment, the pacemaker determines QT interval, and stores data representative of changes in QT interval as a function of paced heart rate and/or the patient""s spontaneous lower rate when at rest. Variations in the correlation of QT interval and heart rate, and/or variations in patient lower rate at rest are processed to provide a time trend, or profile, from which a determination is made as to whether or not LVD is indicated. In alternate embodiments, other data derived from cardiac signals is processed and stored, e.g., QRS width, T-wave amplitude, etc. A change in the variation of T-wave amplitude with respect to exercise, and consequent heart rate, can be easily measured and tracked in a QT rate responsive pacemaker, or any pacemaker adapted to sense and recover the T-waves. Likewise, as noted above, changes in QRS duration (width) and/or morphology may also be detected and tracked for detection of a trend. Trends in this data are periodically evaluated, e.g., on a daily basis, and stored for downloading to an external programmer for deriving an indication of LVD, or onset or progression of LVD or for automatic initiation of a treatment response signals.
An algorithm for automatically adjusting the rate responsive parameters, i.e., the correlation function between QT and desired rate is suitably performed on a daily basis. The pacemaker measures a slope of the correlation function at the LRL, and adjusts the QT-rate function between LRL and URL accordingly as disclosed in commonly assigned U.S. Pat. No. 4,972,834. If such changes are stored and analyzed for a trend, progress toward LVD can be indicated. Likewise, if it is found that the patient heart rate is not dropped to the programmed LRL during nighttime, such that the spontaneous lower rate has had an upward progression, this trend can also be used as an indicator of the onset of LVD.
As asserted in the ""744 patent, these functions can be performed in an implanted monitor solely dedicated to detection and storage of cardiac data and processing of such data to provide an indication of LVD when interrogated. In a more preferred embodiment, a rate responsive pacemaker system is disclosed that can pace and sense in any combination or all of the four cardiac chambers. The treatment response upon an indication of onset of LVD has a number of embodiments, including changing the rate response function; changing physiologic sensor blending for dual or plural sensor rate responsive pacemakers; initiating three or four chamber pacing to achieve improved left heart response, e.g., synchronous ventricular pacing and/or other multi-chamber sequential pacing; and providing for a measured release of an appropriate drug for treating the LVD. In yet another disclosed embodiment, the pacemaker is implanted with software for carrying out normal dual chamber pacing, but the software can be upgraded by programmer downloading to provide different pacing functions, or to function as a three or four chamber pacemaker, along with utilization of an additional lead or leads for delivering stimulus pulses to the left heart chambers.
Chronically collected data from patients with heart failure is needed so that the treating cardiologist can properly and accurately chart the progression, determine the nature of the heart failure, and be able to implement the optimal treatment in a timely fashion. There is a substantial need in the art for a pacemaker or other implanted device having the capacity to identify the progression or remission of heart failure and to provide such indication to the patient""s physician so that options can be assessed from time to time to treat the changing patient condition.
In view of the above need, the present invention provides a system and method for monitoring patient cardiac signals and processing such signals within an implantable medical device (IMD) to provide data from which the onset or progression of heart failure can be determined. It is to be understood that the invention is applicable to various forms of heart failure, including left heart conduction disorders such as IAB, LBBB and RBBB, and other forms of heart dysfunction including LVD.
The present invention is implemented in a wide variety of ways. In the broadest context, the present invention pertains to cardiac pacing systems that pace and sense in at least a first site in the heart and sense conducted electrical signals at a second site in the heart and measuring and accumulating electrical conduction times between the first and second sites to derive trend data indicative of the state of heart failure. The present invention is preferably embodied in a multi-site, cardiac pacing system having memory for storing such conduction time data.
The first and second sites can be separated sites in a single heart chamber of right heart chamber (RHC) and left heart chamber (LHC) sites, e.g., right and left atrial (RA and LA) sites or right and left ventricular (RV and LV) sites. In a conduction measurement operating mode, one or both of the RHC-LHC and LHC-RHC conduction times are measured and conduction time data is stored in memory along with a date and time stamp and any other data of interest. A series of RHC-LHC and LHC-RHC conduction times can be measured and processed to determine maximum, minimum and average RHC-LHC and LHC-RHC conduction times that are stored in memory.
The RHC-LHC and LHC-RHC conduction time measurements can be made from intrinsic sense events at the first RHC or LHC site to an intrinsic sense event at the second LHC and RHC, respectively, site. Preferably, the first site is paced at the time-out of a pacing escape interval or upon a sense event. In this way an RHP-LHC conduction time is measured from an RHC pace (RHP) pulse to an LHC sense (LHS) event and an LHP-RHC conduction time is measured from an LHC pace (LHP) pulse to an RHC sense (RHS) event. The RHP-LHC conduction time can be compared with the LHP-RHC conduction time in the assessment of the heart failure state.
In one preferred embodiment, a multi-site, cardiac pacing system is provided wherein ventricular pacing pulses are delivered to first and second ventricular sites synchronously within a V-V pace delay at a predetermined pacing rate in accordance with the steps of and means for: (a) timing a ventricular pacing escape interval; (b) detecting a ventricular depolarization in a selected one of the first and second ventricular sites within the pacing escape interval and, in response, terminating the pacing escape interval and providing a first ventricular sense (VS) event; (c) delivering a first ventricular pace (VP) pulse to the selected one of the first and second ventricular sites upon either the time-out of the pacing escape interval without provision of a first VS event or upon provision of the first VS event during time-out of the pacing escape interval; (d) timing the V-V pace delay from a first VS event occurring prior to the time-out of the pacing escape interval or from a first VP pulse delivered either upon provision of the first VS event or upon time-out of the pacing escape interval; and (e) delivering a second VP pulse to the other of the first and second ventricular sites upon the time-out of the V-V pace delay.
In accordance with the present invention, an interventricular V-V conduction time measurement mode is entered periodically to measure the V-V conduction time between the first and second ventricular sites. Steps (d) and (e) can be suspended or the measurement can take place when there is a V-V conduction time that is shorter than the prevailing V-V pace delay. The V-V conduction time is measured from a VS event or VP pulse delivered to the selected one of the first and second ventricular sites to the VS event at the other one of the first and second ventricular sites, and the measured V-V conduction time is stored in memory. The measured V-V conduction time can be one or more of a VS-VS conduction time, a VP-VS conduction time and a VS/VP-VS conduction time. In each case, a single data point measured V-V conduction time may be obtained and stored or the high and low measured V-V conduction times and an average V-V conduction time can be obtained from a series of measured V-V conduction times. The measured V-V conduction time (or times if more than one mode is entered) as well as related data including a date and time stamp of the measurement event, the prevailing heart rate, and the activity level of the patient or other indicator of physiologic need for cardiac output are stored in IMD memory for subsequent analysis. Trend data evidencing any change in the intrinsic conduction time between the first and second ventricular sites gathered over a period of days, weeks and months provides a valuable indication as to whether the heart failure state is improving, worsening or staying about the same.
More particularly, a method and apparatus is provided that periodically derives trend data representative of the state of heart failure as evidenced by the V-V conduction time between the first and second ventricular sites by the steps of or means for: (f) suspending steps (d) and (e) while steps (a) through (c) are performed for one or more heart cycle; (g) detecting a ventricular depolarization in the other of the first and second ventricular sites during the one or more heart cycle and providing a second VS event in response; and (g) measuring and storing in memory one of the elapsed VS-VS conduction time from a first VS event or the elapsed VP-VS conduction time from the first VP pulse delivered at the end of the pacing escape interval or the elapsed VS/VP-VS conduction time from the first VP pulse delivered upon a first VS event occurring during the time-out of the pacing escape interval, whereby trend data representative of the state of heart failure as evidenced by changes in the stored one of the elapsed VS-VS conduction time, the VP-VS conduction time, and the VS/VP-VS conduction time between the first and second ventricular sites is accumulated for analysis of the trend.
The present invention is preferably embodied in a multi-site, AV sequential, cardiac pacing system wherein ventricular pacing pulses are delivered to the right and left ventricles synchronously within a V-V pace delay following time-out of an AV delay from a preceding delivered atrial pace pulse or an atrial sense event and operating in accordance with the steps of: (a) timing an AV delay from a preceding delivered atrial pace pulse or an atrial sense event; (b) detecting a ventricular depolarization at one of a first and second ventricular site within the AV delay and, in response, terminating the AV delay and providing a ventricular sense event; (c) delivering a ventricular pace pulse to a selected one of the first and second ventricular sites upon the time-out of the AV delay; (d) timing the V-V pace delay from a ventricular sense event occurring prior to the time-out of the AV delay or from a ventricular pace pulse delivered at the end of the AV delay; and (e) delivering a ventricular pace pulse to the other of the first and second ventricular sites upon the time-out of the V-V pace delay.
In one variation, the conduction time measurement mode causes the triggered pacing mode to be entered wherein step (b) is modified by delivering a VP pulse to the selected one of the first and second ventricular sites upon the a VS occurring during the time-out of the AV delay or during the V-A escape interval, steps (d) and (e) are suspended, and a measurement of the intrinsic VP-VS conduction time elapsing from the delivery of the ventricular pace pulse to the selected one of the first and second ventricular sites and the detection of the conducted depolarization in the other of the first and second ventricular sites is made and stored in memory.
In a further variation, the triggered pacing mode is not entered, and the intrinsic ventricular rate examined to ensure that it is above the programmed LRL such that the ventricular depolarization consistently falls within the prevailing AV delay and inhibits delivery of a ventricular pacing pulse at the timeout of the AV delay. Steps (d) and (e) are suspended, the elapsed VS-VS conduction time between the sensed ventricular depolarization at one of the first and second ventricular sites and the subsequent ventricular depolarization at the other one of the first and second ventricular sites is measured, and the elapsed VS-VS conduction time is stored in memory.
In a still further variation, an overdrive pacing mode is entered that synchronously paces the atrial chamber and the selected one of the first and second ventricular sites at a rate exceeding the prevailing intrinsic heart rate to ensure capture. Steps (d) and (e) are suspended, and a measurement of the intrinsic VP-VS conduction time elapsing from the delivery of the ventricular pace pulse to the selected one of the first and second ventricular sites and the detection of the conducted depolarization in the other of the first and second ventricular sites is made and stored in memory. Optionally, only the selected ones of the first and second ventricular sites could be paced at the overdrive pacing rate.
The first and second ventricular sites preferably comprise RV and LV pace/sense electrode sites, and RV event and LV event signals are sensed at the RV and LV pace/sense electrodes. Preferably, the selected one of the RV and LV that a ventricular pace pulse is delivered to is the RV, and the ventricular depolarization is sensed in the LV to determine a VS/VP-VS or VP-VS RV-LV conduction time. However, in each of the above embodiments, the measurement operating mode can be repeated to deliver a ventricular pace pulse is to the LV, and the ventricular depolarization is sensed in the RV to determine a VS/VP-VS or VP-VS LV-RV conduction time.
This summary of the invention has been presented here simply to point out some of the ways that the invention overcomes difficulties presented in the prior art and to distinguish the invention from the prior art and is not intended to operate in any manner as a limitation on the interpretation of claims that are presented initially in the patent application and that are ultimately granted.